nofollow is a setting on a web page hyperlink that directs search engines not to use the link for page ranking calculations. It is specified in the page as a type of link relation; that is:. Because search engines often calculate a site's importance according to the number of hyperlinks from other sites, the setting allows website authors to indicate that the presence of a link is not an endorsement of the target site's importance.

Concept and specification

The value was originally suggested to stop comment spam in blogs. Believing that comment spam affected the entire blogging community, in early 2005 Google's Matt Cutts and Blogger's Jason Shellen proposed the value to address the problem. The specification for is copyrighted 2005–07 by the authors and subject to a royalty-free patent policy, e.g. per the W3C Patent Policy 20040205, and IETF.

Example

Introduction and support

Google announced in early 2005 that hyperlinks with would not influence the link target's PageRank. In addition, the Yahoo and Bing search engines also respect this attribute value. On June 15, 2009, Google software engineer Matt Cutts announced on his blog that GoogleBot changed the way it treats nofollowed links, in order to prevent webmasters from using nofollow for PageRank sculpting. Prior to this, webmasters would place nofollow tags on some of their links in order to maximize the PageRank of the other pages. As a result of this change, the usage of nofollow leads to the evaporation of the pagerank of outgoing normal links as they started counting total links while calculating page rank. The new system divides page rank by the total number of outgoing links irrespective of nofollow or follow links, but passes the page rank only through follow or normal links. Cutts explained that if a page has 5 normal links and 5 nofollow outgoing links, the page rank will be divided by 10 links and one share is passed by 5 normal links. However, as of March 1 2020, Google is treating the nofollow link attribute as a hint, rather than a directive, for crawling and indexing purposes.

Interpretation by the individual search engines

While all engines that use the value exclude links that use it from their ranking calculation, the details about the exact interpretation of it vary from search engine to search engine.

Use by websites

Many weblog software packages mark reader-submitted links this way by default (often with no option to disable it, except for modification of the software's code). More sophisticated server software could suppress the nofollow for links submitted by trusted users like those registered for a long time, on a whitelist, or with an acceptable karma level. Some server software adds to pages that have been recently edited but omits it from stable pages, under the theory that stable pages will have had offending links removed by human editors. The widely used blogging platform WordPress versions 1.5 and above automatically assign the attribute to all user-submitted links (comment data, commenter URI, etc.). However, there are several free plugins available that automatically remove the attribute value. Social bookmarking and photo sharing websites that use the tag for their outgoing links include YouTube and Digg.com (for most links); websites that don't use the tag include Yahoo! My Web 2.0, Technorati Favs, and Propeller.com (no longer an active website).

Repurpose

Control internal PageRank flow

Search engine optimization professionals started using the attribute to control the flow of PageRank within a website, but Google has since corrected this error, and any link with a nofollow attribute decreases the PageRank that the page can pass on. This practice is known as "PageRank sculpting". This is an entirely different use than originally intended. was designed to control the flow of PageRank from one website to another. However, some SEOs have suggested that a used for an internal link should work just like used for external links. Several SEOs have suggested that pages such as "About Us", "Terms of Service", "Contact Us", and "Privacy Policy" pages are not important enough to earn PageRank, and so should have on internal links pointing to them. Google employee Matt Cutts has provided indirect responses on the subject, but has never publicly endorsed this point of view. The practice is controversial and has been challenged by some SEO professionals, including Shari Thurow and Adam Audette. Site search proponents have pointed out that visitors do search for these types of pages, so using on internal links pointing to them may make it difficult or impossible for visitors to find these pages in site searches powered by major search engines. Although proponents of use of on internal links have cited an inappropriate attribution to Matt Cutts (see Matt's clarifying comment, rebutting the attributed statement) as support for using the technique, Cutts himself never actually endorsed the idea. Several Google employees (including Matt Cutts) have urged Webmasters not to focus on manipulating internal PageRank. Google employee Adam Lasnik has advised webmasters that there are better ways (e.g. click hierarchy) than to "sculpt a bit of PageRank", but that it is available and "we're not going to frown upon it". YouTube, a Google company, uses nofollow on a number of internal "help" and "share" links.

Qualified outbound links

On September 10, 2019, Google announced two additional ways for webmasters to qualify the relationship of outbound hyperlinks. The attribute may be used to denote links that are advertisements, sponsorships or other compensation agreements. The attribute, standing for "User-generated content", may be used to denote content such as user-contributed comments and forum posts. Additionally, the attributes may be combined, such as, denoting a link that was both user-generated and sponsored. In 2019, WordPress announced plans to convert all blog comments into rel="ugc". These "hint" link attributes address some of the criticisms of by allowing webmasters to denote outbound links that lack "the weight of a first-party endorsement", but are not necessarily spam.

Blocking and excluding content from search engines